The generic data base is a registry of baseline and outcome data for all infants with birth weights from 401 to 1,500 grams, inclusive, who are admitted to the neonatal intensive care unit within 14 days of birth or who died in the delivery room of the 14 institutions participating in the NICHD Neonatal Research Network. These centers serve varying populations and exemplify the morbidity problems of the low birth weight neonate but the registry is not representative of a regional sample.